Biomedical subjects

Anna Montagnini

Publications and source records attributed to Anna Montagnini.

4 recordsLinked to original sources

PubMed2006

Predicting 2D target velocity cannot help 2D motion integration for smooth pursuit initiation.

Smooth pursuit eye movements reflect the temporal dynamics of bidimensional (2D) visual motion integration. When tracking a single, tilted line, initial pursuit direction is biased toward unidimensional (1D) edge motion signals, which are orthogonal to the line orientation. Over 200 ms, tracking direction is slowly corrected to finally match the 2D object motion during steady-state pursuit. We now show that repetition of line orientation and/or motion direction does not eliminate the transient tracking direction error nor change the time course of pursuit correction. Nonetheless, multiple successive presentations of a single orientation/direction condition elicit robust anticipatory pursuit eye movements that always go in the 2D object motion direction not the 1D edge motion direction. These results demonstrate that predictive signals about target motion cannot be used for an efficient integration of ambiguous velocity signals at pursuit initiation.

Eye Movements↗

PubMed2006

Dynamics of attentional deployment during saccadic programming.

The dynamics of attentional deployment before saccade execution was studied with a dual-task paradigm. Observers made a horizontal saccade whose direction was indicated by a symbolic precue and had to discriminate the orientation of a Gabor patch displayed at different delays after the precue (but before saccade onset). The patch location relative to the saccadic target was indicated to observers before each block. Therefore, on each trial, observers were informed simultaneously about the respective absolute locations of the saccadic and perceptual targets. The main result is that orientational acuity improved over a period of 150-200 ms after the precue onset at the saccadic target location, where overall performance is best, and at distant locations. This effect is due to attentional factors rather than to an alerting effect. It is also dependent on the efficiency of the temporal masks displayed before and after the Gabor patches.

Attention↗

PubMed2005

The urgency to look: prompt saccades to the benefit of perception.

Researchers have shown that the promptness to initiate a saccade is modulated by countless factors pertaining to the visual context and the task. However, experiments on saccadic eye movements are usually designed in such a way that oculomotor performance is dissociated from the natural role of saccades, namely that of making crucial perceptual information rapidly available for high-resolution, foveal analysis. Here, we demonstrate that the requirement to perform a difficult perceptual judgment at the saccade landing location can reduce saccadic latency (by >15%) and increase saccadic peak velocity. Importantly, the effect cannot be explained in terms of arousal, as latency changes are specific to the location where the perceptual judgement is required. These results indicate that mechanisms for voluntary saccade initiation are under the powerful indirect control of perceptual goals.

Adult↗

PubMed2003

The evolution of mammalian cortex, from lamination to arealization.

We analyse some of the most important anatomical and functional features emerging at different stages of mammalian brain evolution in terms of a possible computational advantage. At the transition from reptiles to mammals, a major anatomical change occurs in the originally sensory dorsal cortex. The principal layer of pyramidal cells is split by the insertion of a new layer of granule cells, giving rise to the laminated isocortex. It has been hypothesized that this qualitative change in the evolution of mammalian brains is necessary to support fine topography in their sensory maps. The simulation of neural network models demonstrates that a nonlaminated patch of cortex must compromise between transmitting "where" information, explicitly mapped, topographically, on the cortical sheet, and retrieving "what" information, represented by the distributed firing pattern across neurons. The differentiation of a granular layer is shown in the model to yield a small quantitative advantage, allowing to transmit a slightly better combination of both information types. Along the same theoretical lines, we are investigating the multiplication of successive sensory areas coding for ever more composite stimuli, such as those in the visual and auditory temporal cortices in primates. In particular we analyse the possible computational advantage for a specific neural population devoted to encode the complex structure of whole stimuli, rather than relying on the coactivation of separate populations encoding their basic elements.

Animals↗